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Ectomycorrhizal (ECM) fungi form important functional and biomass components of forest soils. They serve roles in nutrient cycling, maintenance of soil structure, nutrient uptake by seedlings, plant to plant interactions belowground, and as food sources for soil invertebrates and small mammals. The hyphae of ectomycorrhizal fungi are estimated to comprise at least 30% of the microbial biomass in boreal forest soils (Högberg and Högberg 2002). Most commercially important conifers do not grow normally in the absence of ECM associations. There are estimated to be as many as 15,000 different species of ectomycorrhizal fungi, with different physiologies (Hutchison 1990), preferences for soil microsites (Genney et al. 2006, Rosling et al. 2003; Tedersoo et al. 2003), and abilities to disperse via spores vs. hyphae (Deacon & Fleming 1992). Hence, it is hypothesized that trees colonized by a number of functionally diverse ECM fungi are better able to exploit the wide array of organic and inorganic sources of nutrients present in forest soils. A major review by Jones et al. (2003) concluded that clearcut harvesting rarely has an effect on the rate at which new seedlings become colonized by mycorrhizal fungi, but always causes a change in the ECM fungal community. This shift in fungal species seems to be driven in large part by a reduction in the availability of effective inoculum of some fungi. In particular, because some ECM fungi cannot disperse vegetatively once their host tree is dead, fungi that can disperse by spores tend to dominate over fungi that disperse by root-to-root growth (Hagerman et al 1999b). This is a concern if it means that seedlings no longer have access to the full spectrum of ECM fungi previously present on a site. In addition to differences in inoculum, it is likely that changes in environmental conditions after harvest are also responsible for some of the species shifts (Jones et al. 2003). Here we propose to determine whether retention of coarse wood debris during clearcut logging encourages the retention of some members of the ECM fungal community. Although generally thought to be totally dependent on their hosts, some ECM fungi also have a limited ability to live saprotrophically (Erland & Söderstrom 1991). If retention of coarse woody debris (CWD) allows these fungi to remain active on a site, this stand-level treatment can increase overall functional biodiversity of the soil microflora. Coarse woody debris or downed wood is widely recognized as an important component of forest ecosystems. Therefore forest certification criteria often include a requirement that coarse woody debris be retained on site after harvesting (e.g., Forest Stewardship Council 2005). The argument for retaining coarse woody debris typically involves arguments about the maintenance of animal biodiversity (Jonsson et al 2006), however major questions remain about the effectiveness of coarse woody debris in achieving these goals. For example, the FRPA Resource Evaluation Program lists the following question as the second highest in importance: 'Is the structural retention (WT and CWD) left associated with cutblocks adequately maintaining habitat for dependent species at the site and across the landscape now and in the future?' (https://www.for.gov.bc.ca/hfp/frep/4_frep_pe_questions.html; April 2006). There is rarely any attention paid to the importance of CWD in influencing soil biodiversity, and yet soil factors and associated ecosystem functions are always highly ranked in sustainability criteria. This lack of information on soil was highlighted in a recent FORREX workshop (Leech 2006). We hypothesize that coarse woody debris will increase ECM diversity because downed wood supports a high density of ectomycorrhizas (Harvey et al. 1978, 1979; Christy et al. 1982; Vogt et al. 1995) with some types of ectomycorrhizas found exclusively in coarse woody debris (Goodman & Trofymow, 1998, Tedersoo et al 2003). Different ECM fungi play ...
Jones, Melanie D.. 2007. Does retention of downed wood help maintain stand-level functional biodiversity of mycorrhizal fungi in EESF clearcuts?. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2007MR293
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), Mycorrhizal, Fungi, British, Columbia
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